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elec wtr htr, concrete floor

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billygoat400
billygoat400 Member Posts: 9

been a few yrs since was last here, computer forgot who I was..

maybe can't (or shouldn't) be done- customer wants to hook up his radient heat in floor. concrete floor room w/carpet 18x18, and garage floor, bare concrete.

has an elec water heater, each zone has one loop each of 1/2" sticking out floor in mech room. aside from the issue of what length and spacing, the elec htr and load calc,

I'm wondering how you would set the temps for the two zones? set the hw for carpeted zone and mixing/3 way valve for garage? he has a geo hp, and wants to add some heat for the two basement rooms.

piping was existing before I ever showed up.

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  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,176
    edited May 16
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    According to your statement, there is piping PEX tubing in the concrete floor already

    "piping was existing before I ever showed up."

    Also has an electric water heater

    has an elec water heater,

    And you don't know the amount of tubing in the floor or the spacing of the tubing.

    Then with a statement in your agreement to do the work, in big print state: "that by connecting the pipes from the floor to any heat source does not necessarily mean that the heat provided will be adequate for the space."

    Next thing would be that the water heater you connect the heating pipes to will not be used for potable water or Domestic hot water use. It must be a separate water heater piped as a. closed system with a pressure relief valve that releases at no higher than 30 PSI, an expansion tank and a backflow preventer that separates the closed system from the porable water system of the building.

    If the customer wont sign that, then walk away

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    Alan (California Radiant) Forbes
  • ratio
    ratio Member Posts: 3,701
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    @EdTheHeaterMan has the important part: "If the customer wont sign that, then walk away "

    Cheapo job like this are a landmine waiting to bite you on the a$$.

    EdTheHeaterMan
  • hot_rod
    hot_rod Member Posts: 22,491
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    i would have you do a heat load calc first, for each riom

    324 sq feet at 20 btu/ sq ft would be 6480btu/ hr. That us doable if there is enough tube in the floor


    Fill the tube with water and measure the amount to get a close number on footage in the slab

    An electric water heater with typical 4500w element gets you 15,000 btu/hr

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • Alan (California Radiant) Forbes
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    What is the capacity of the water heater? 240V?

    8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

    Two btu per sq ft for degree difference for a slab
  • hot_rod
    hot_rod Member Posts: 22,491
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    if the room is 324 square feet, the single loop would need to be 350’ to give you 12” on center spacing, which is fairly wide for comfortable residential floor surface temperatures.

    Also a 350’ loop tends to lose heat at the loops end. Ideally two shorter loops would have been nice, two 200’ loops for example.

    To many unknowns to give a good answer. Room load, tube spacing, slab depth and tube location in the slab, underslab insulation detail, etc.

    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    EdTheHeaterMan
  • billygoat400
    billygoat400 Member Posts: 9
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    customer has a water heater there, not connected. agree on the "in writing" issue. he has a geothermal unit he bought online that's been my personal nightmare to keep replacing parts on.

    I expect the cost of controls, pump, valves , etc would put him off, anyway. I'd like to do some radiant, maybe he knows what is in floor.

    like the adding water idea to gauge the tubing length.